Apparatus and method for manufacturing a wrapped endless rod of substantially flat continuous material

ABSTRACT

The method for manufacturing a wrapped endless rod of substantially flat continuous material comprises the steps of providing a substantially flat continuous material, treating the substantially flat continuous material with corona discharge and forming the corona treated substantially flat continuous material into an endless rod. Further steps comprise providing a wrapper, applying adhesive to the wrapper and wrapping the endless rod with the wrapper. Therein the step of applying adhesive to the wrapper comprises applying adhesive over a width of the wrapper and in a central portion of the wrapper.

The invention relates to an apparatus and method for manufacturing a wrapped endless rod of substantially flat continuous material. Especially, it relates to an apparatus and method for use in the manufacture of aerosol generating articles or smoking articles or their components.

Aerosol generating articles or their components such as, for example, filter plugs are generally manufactured at least partially from a substantially flat continuous material, such as a paper, tobacco or plastic web. The flat continuous material is subsequently formed into an endless rod. The endless rod is wrapped into a wrapper. The wrapper has been provided with glue to close the wrapper and secure the wrapper to the endless rod. Due to the special materials used for the production of plugs, especially plastics materials, and the high production speed these plugs are manufactured, the plugs may tend to displace or fall out of their wrappers. This is particularly pronounced where the rod shaped products or semi products have a sudden change in transport direction, for example from a movement in the direction of the longitudinal extension to a movement transverse to this direction. Unsecured segments may dislodge due to inertia in the first direction of travel. This may lead to blockage of the production line. It may also set limits to a production speed or negatively impact the operation of the final rod shaped product.

Thus, there is a need for an apparatus and method for manufacturing wrapped endless rods of substantially flat continuous material for use in the production of aerosol-generating articles such as smoking articles. Especially, there is a need for an apparatus and method for manufacturing wrapped endless rods of substantially flat continuous material having improved anchoring of a rod material to its wrapper.

According to an aspect of the invention, there is provided an apparatus for manufacturing a wrapped endless rod of substantially flat continuous material. The apparatus comprises a rod-forming unit for shaping a substantially flat continuous material into an endless rod. The apparatus also comprises a wrapping device for providing a wrapper and for wrapping the endless rod with the wrapper. An adhesive applicator is provided for applying an adhesive to the wrapper before wrapping the endless rod. The apparatus further comprises a corona module arranged upstream of the rod-forming unit for corona treating the substantially flat continuous material.

In the corona module, the substantially flat continuous material is corona treated. By the corona treatment, the wetting characteristic of at least one side of the continuous material is improved. By this, an adhesive applied later or further downstream in the apparatus, respectively, better wets the continuous material and spreads over an extended portion of the continuous material compared to the same non-corona treated material. When wrapping the wrapper around the rod-shaped continuous material, the adhesive then contacts the material of the rod not only in small limited spots but in extended areas of adhesive. This improves the anchoring of the rod material to its wrapper. Thus, the risk of longitudinal and rotational displacement of the rod material in the wrapper may be reduced or prevented. Thus, an inadvertent displacement or loss of the rod material in or from its wrapper may be prevented or its occurrence reduced. This is particularly advantageous at high production speed and when using materials having low relative adhesion, such as for example paper and plastics materials.

The adhesive applicator may be arranged for applying adhesive in a specific pattern and location onto the wrapper, preferably to a central portion of the wrapper as will be described in more detail below relating to the method. Preferably, an apparatus is then programmed to perform such a method.

In addition, the corona treatment has little permanent impact on the product characteristics due to a disappearing of the effect typically after several days. Also little mechanical modification of a treated material occurs during corona treatment. Since no chemicals are required for a corona treatment, no unintended residual of chemicals remains in or on a product incorporating the material that has been treated by the corona field.

Depending on the materials used for the wrapper, a corona treatment may also improve adhesion of the wrapper material to itself, in particular if the wrapper material is also corona treated. Thus, also the creation of a reliable seam of the wrapper may be supported by the corona treatment.

Since adhesives are generally materials, which are required for the manufacturing process but not necessarily required or desired in a final product, the amount of adhesive shall be kept at a minimum. Through better adhesion and spreading of the adhesive after corona treating of the rod material, an amount of adhesive may possibly be limited and still have improved anchoring than in wrapped endless rods of substantially flat continuous material that have been manufactured without the additional corona treatment.

Corona treatment is an as such known electrochemical process for surface modification, especially of plastics materials such as polyethylene-, polypropylene- and polyester foils. Corona treatment is performed to enhance the wettability of a surface, for example for printing liquids. The base material, that is the material that will be treated by the corona treatment, is exposed to high voltage discharge occurring between an electrode and a counter-electrode, the latter typically being at ground potential. Through corona treatment surface tension of the treated material is altered through ionization of the fluid surrounding the base material. If the base material abuts the counter-electrode, only the side of the base material facing the electrode at high voltage is treated. Generally, the electrode is powered by a high frequency generator with alternating voltage between 10 to 20 kV and a frequency between 10 and 60 kHz.

According to an aspect of the apparatus according to the invention, a shape of an electrode or of a counter electrode of the corona module corresponds to the surface of a guiding element the substantially flat continuous material is guided along in the corona module. In such an embodiment, the continuous material is guided on or over the guiding element, while passing the corona module. The guiding element may directly serve as electrode or counter electrode. Preferable, the guiding element is a counter electrode. Preferably, the counter electrode is electrically isolated. Preferably, the counter electrode is held at ground potential. If the substantially flat continuous material is in direct contact with the guiding element, for example a guiding drum, the side of the continuous material contacting the guiding element is not corona treated. In this set-up, only the side of the continuous material facing the electrode is corona treated.

The use of a guiding element may further simplify the handling and changeover of base material during or between production runs. The corona module may be adapted to different material, however, with unchanged geometric conditions. Preferably, the continuous base material is guided through the corona module continuously and preferably at a constant speed while the corona module is active, that is while the continuous material is corona treated. However, a base material may also be transported into the corona module, placed between the electrode and counter electrode and be corona treated while being stationary. Preferably, a subsequent continuation of transport of the base material is performed using a speed ramp in order to prevent abrupt pulling on the continuous material.

Corresponding forms of electrode and counter electrode allow for a defined, preferably constant, distance between electrode and counter electrode.

A distance between electrode and counter electrode may be in a range between 0.1 millimeter and about 25 millimeter. A distance between electrode and counter electrode may preferably be in a range between 1 millimeter and about 10 millimeter, for example 8 millimeter.

In some preferred embodiments, an electrode of the corona module has a lateral size corresponding to a width of the substantially flat continuous material to be corona treated. A size of the electrode may be adapted to a size or area of the continuous material to be corona treated. If the continuous material is corona treated over an entire width of the material, a wetting characteristic of an entire side of the continuous material may be improved. Thus, an adhesive on a wrapper coming into contact with the continuous material, preferably corona treated, is substantially independent on the location where the continuous material and the wrapper contact each other. Thus, an anchoring of continuous material to the wrapper may be made more reliable and more flexibility in adhesive application may be achieved. For example, locations on the wrapper that are provided with adhesive are substantially independent with respect to the arrangement of the substantially flat continuous material when gathered into rod-shape.

According to another aspect of the apparatus according to the invention, the corona module comprises a first module portion and a second module portion, wherein the first module portion and the second module portion each comprise an electrode-counter electrode pair. The electrode-counter electrode pair of the first module portion is arranged and powered to enable corona treatment of one side of the substantially flat continuous material. The electrode-counter electrode pair of the second module portion is arranged and powered to enable corona treatment of the other side of the substantially flat continuous material.

To enable corona treatment of both sides of a base material, the base material is guided through two corona module portions, wherein the base material is corona treated. Each module portion has an electrode-counter electrode pair. While corona treatment of two sides of a foil or flat material is basically also possible in a corona module having one electrode-counter electrode pair only, a two-sided treatment is preferably performed with two subsequently arranged electrode-counter electrode pairs. One pair may then be optimized to the treatment of one side such that after the base material leaves the corona module, both sides have reliably been corona treated in the corona module. If both sides of the base material are corona treated, a position of a contact area between rod material and wrapper (and thus the location of adhesive on the wrapper) becomes entirely independent on the location of an adhesive on the wrapper and on the folding of the continuous material into a rod. For example, a seam line or an adhesive may be positioned anywhere on the circumference of the rod and a flat material may be gathered to a rod shape in a well-defined manner or completely irregularly: the adhesive on the wrapper will always come into contact with a corona treated (side of the) rod material.

According to a further aspect of the apparatus according to the invention, the corona module comprises a high frequency generator for providing frequencies in a range between 10 kHz and 60 kHz and an alternating voltage between 15 kV and 40 kV.

These frequency and voltage ranges have shown to provide good adhesive wetting for the materials as used in the manufacture of plugs for smoking articles, aerosol generating articles or their components. In addition, these operation ranges of frequency and voltage provided good results without damaging the materials, especially plastics materials, such as, for example, polylactic acid webs.

Substantially flat continuous materials may be continuous material selected from the group consisting of polyethylene (PE), polypropylene (PP), polyvinylchloride (PVC), polyethylene terephthalate (PET), cellulose acetate (CA), and aluminium foil or any combination thereof. Preferably, a substantially flat continuous material as used in the method according to the invention has a width of between about 150 millimeter and about 270 millimeter. In some preferred embodiments, the substantially flat continuous material is a plastics material, for example polylactic acid (PLA). A polylactic acid sheet may have a thickness between about 10 microns and about 250 microns, preferably about 50 microns plus or minus 5 microns.

A wrapper may be a continuous web of paper, plastics or metal as may be used in the manufacture of smoking articles or aerosol-generating articles. Preferably, a wrapper is a paper wrapper. A wrapper may have a thickness between 20 microns and 250 microns, preferably between 40 microns and 180 microns.

According to the invention, there is also provided a method for manufacturing a wrapped endless rod of substantially flat continuous material. The method comprises the steps of providing a substantially flat continuous material and treating the substantially flat continuous material with corona discharge. The method further comprises the steps of shaping the corona treated substantially flat continuous material into an endless rod, providing a wrapper, applying adhesive to the wrapper, and wrapping the endless rod with the wrapper provided with the adhesive. Preferably, the step of applying adhesive to the wrapper comprises applying adhesive over a width of the wrapper and in a central longitudinal portion of the wrapper. As used herein, the central longitudinal portion is understood to include a central longitudinal axis of the wrapper and about plus or minus 50 percent of the entire width of the wrapper.

Adhesive is applied in the central longitudinal portion according to a regular or irregular pattern. Preferably, adhesive is not applied over the entire central longitudinal portion but over one or several limited areas in the central longitudinal portion.

Adhesive applied in the central longitudinal portion is provided for coming into contact with the rod material, that is, with the gathered or folded corona treated flat material. Adhesive is also applied in a seam region, for adhering the wrapper to itself and forming a seam. A seam region typically covers a few percent of the width of a wrapper only. Adhesive application in a central longitudinal portion and in a seam region may be combined in one application step. For example, a glue pattern may extend from the central longitudinal portion to the seam region. Adhesive application in a central longitudinal portion and in a seam region may be provided in separate adhesive application steps, for example by separate applicator movements or separate applicators or both separate movements and separate applicators.

According to an aspect of the method according to the invention, the method comprises the step of guiding the substantially flat continuous material between electrode and counter electrode of a corona module.

A corona treatment of the substantially flat continuous material may be performed during a treatment time in a range between 0.001 seconds and 2 seconds, preferably in a range between 0.02 seconds and 0.5 seconds. These corona treatment times have shown to increase an adhesion force between the corona treated material and a wrapper glued to the corona treated material particularly well. Preferably, the mentioned treatment times are applied in a corona module having frequency and voltage ranges as mentioned above.

Preferably, during a treatment time, the substantially flat material is continuously transported through and between electrode and counter electrode. If two sides of the substantially flat continuous material are treated in two subsequent corona module portions, a corona treatment may be performed in each of the module portions during an above mentioned treatment time.

In some preferred embodiments of the method according to the invention, the method comprises the step of corona treating one side of the substantially flat continuous material and then subsequently corona treating the other side of the substantially flat continuous material.

Advantages and further aspects of the method according to the invention have been described relating to the apparatus according to the invention and will therefore not be repeated.

According to a further aspect of the method according to the invention, the step of applying an adhesive to the wrapper comprises applying the adhesive over a length or over a width or over a length and a width of the wrapper. In particular, the step of applying an adhesive to the wrapper comprises applying the adhesive in one or several strips over a length or over a width or over a length and a width of the wrapper. For example, one longitudinal strip may be applied in the central longitudinal portion of the wrapper and one longitudinal strip of adhesive may be applied to the seam region.

Generally, an adhesive is applied longitudinally along the wrapper such that a strip of adhesive, for example glue, is applied and arranged along a side of the wrapper. After wrapping, the portion of the wrapper provided with the strip of glue forms a seam extending parallel to the longitudinal axis of the endless rod. The width of the strip is selected such that the wrapper in the seam region is provided with glue and that to some extent also a portion of the wrapper adjacent to the seam region and facing the rod material is provided with glue. While glue in the seam region is provided for closing the wrapper, the glue facing the rod material is provided for anchoring rod material in the wrapper. A longitudinally arranged strip allows to manufacture a continuously closed wrapper along the longitudinal axis of the endless rod. Typically, two longitudinal strips are arranged along the length of the wrapper: one strip on a lateral side for the seam and one second strip essentially along a longitudinal central axis of the wrapper for the anchoring.

A longitudinally arranged amount of adhesive may also be applied, for example, in the form of a spiral. Such a spiral glue application in a seam region is, for example, described in the European patent EP 1 161 887 B. The application of an adhesive in spiral form has the advantage, among others, that a width of the spiral may easily be adapted to more or less adhesive to come into contact with rod material. In addition, an adhesive applied longitudinally in the form of a spiral also provides the basis for a continuously closed wrapper along the longitudinal axis.

Therein, the glue spiral is described as having the advantage of less adhesive required for achieving a continuously closed wrapper along the longitudinal axis of the seam region of the wrapper.

The term an adhesive extending ‘over a width’ of the wrapper preferably includes adhesive extending over at least 20 percent of the width of the wrapper, more preferably over at least 30 percent of the width, for example over 50 percent of the width of the wrapper. Therein, an adhesive may be a single adhesive area, for example a single strip, or may be a sum of several adhesive areas, for example a sum of several strips arranged in parallel.

In order for an improved anchoring of the rod material and the wrapper, especially to further secure the rod material against rotational displacement inside the wrapper, an adhesive may also be applied to extend over at least part of or entirely around the circumference of the rod. By adhesive application over at least part of the width of a wrapper, preferably at least half of the width, an anchoring of the rod material in the wrapper is further improved. Thus, this may further reduce the risk of or prevent longitudinal and rotational displacement of the rod in the wrapper also at high production speed and also upon using material having low adhesion capability between rod and wrapper material. An adhesive may for example be applied in the form of strips extending transversely over the wrapper, that is, over the width of the wrapper. Preferably, transverse strips are provided as a regular pattern by means of distantly arranged strips. Preferably, transverse strips are applied to the wrapper in a regular sequence. Transverse strips may for example be arranged equidistantly on the wrapper. For example, a transverse strip may be applied at a position where the endless rod will be cut later on into individual segments or plugs. By this, the wrapper will be secured to the rod material, preferably along the entire circumference of the rod, at the ends or at end regions of segments.

A transverse strip may extend over part of the width of the wrapper or over the entire width of the wrapper. In the latter case, adhesive is applied over an entire circumference of the rod in between the wrapper and the rod material.

Adhesive may also be applied over a width and a length of the wrapper thus providing a longitudinal seam as well as a circumferential adhesion of the wrapper to the rod material. Preferably, an adhesive applied over a width and a length in a central longitudinal portion of the wrapper is supplemented by an adhesive applied in a seam region.

The method may comprise the steps of applying one type of adhesive to the central longitudinal portion of the wrapper and another type of adhesive to a seam portion of the wrapper. Different adhesives may, for example differ in settling time or in their application field. If a wrapper is a paper wrapper, paper glue may be used for the seam. If the rod material is a plastics material, for example, specific plastics glue may be used for the anchoring of the wrapper to such plastics rod material.

Preferably, corona treatment is performed on the base material before any further treatments of the material is performed, such as for example crimping, embossing, rolling, electrostatic discharging, cooling, flavoring, gathering and rod-forming. However, corona treatment may also be applied after a treatment step, for example, after one or more of the above mentioned process steps, like for example crimping of the continuous material.

Subsequent treatments may influence the effect of the corona treatment. However, an effect of a corona treatment has been found to last between several hours and several days, depending on the treated material and on the treatment steps. Typical time periods in the apparatus according to the invention passing between corona treatment of the base material and the wrapping of the endless rod formed of the corona treated base material are in a range between fractions of a second up to several minutes. Thus, this time period is well below a time period wherein the effect typically would disappear.

According to the invention, there is further provided a consumable, for example an aerosol-generating article or a smoking article. The consumable comprises a segment, for example a plug, of a wrapped endless rod, which wrapped endless rod has been manufactured according to the method according to the invention and as described herein. Preferably, the plug is a PLA plug, for example, for use as aerosol cooling segment in the consumable. Preferably, the consumable comprises adhesive between a wrapper and a rod material, wherein the adhesive is provided in a central portion of the wrapper, that is, distanced from a seam region of the wrapper.

In the consumable, adhesive may be provided circumferentially between the wrapper and the rod material.

Further processes may be used in combination with corona treatment to improve adhesive application and distribution on a wrapper to improve the attachment of a rod material to its wrapper. Such processes may for example be but are not limited to: variation of adhesives, for example different glues (PVA glues, polar glues); alternative wrapper materials, for example having different wetting characteristic or having different porosity; different glue patterns as the patterns explicitly described herein.

The invention is further described with regard to embodiments, which are illustrated by means of the following drawings, wherein:

FIG. 1 shows a schematic overview of an embodiment of a filter making apparatus including corona module;

FIG. 2 shows a defective semi-finished product;

FIG. 3 shows a corona module;

FIG. 4a,4b show different glue pattern;

FIG. 5 is a measurement set-up for anchoring measurements;

FIG. 6 depicts test results of anchoring measurements.

In the filter making apparatus schematically shown in FIG. 1, a substantially flat continuous material such as a web of material 1 is provided on a bobbin 10. When unwound from the bobbin 10, the web 1 is corona treated, folded and wrapped in the apparatus. In this embodiment, the web 1, for example a PLA film, passes a corona module 2 directly after having been unwound from bobbin 10. In the corona module 2, both sides of the web 1 are subsequently corona treated in two corona module portions 21,22. The corona module 2 is described in more detail with reference to FIG. 3. After corona treatment in the corona module 2, the web 1 passes a crimping device 4, for example a set of two crimping rollers. The crimping device 4 provides the web 1 with a crimping structure, for example with substantially parallel corrugations running, preferably, in longitudinal direction of the web, that is, in transport direction of the web 1. The web 1 then passes a shaping device. The shaping device comprises shaping rollers 50, preferably providing the crimped web 1 with a longitudinally running wave-like macro structure overlaying the crimping micro structure. Imposing the overlaying macro structure onto the web 1 causes the web 1 to be pushed together in a transverse direction of the web. In addition, a gathering of the web 1, for example into a rod shape, is supported by the longitudinal wave-like structure and may be performed in a more controlled manner. The shaping device also comprises a funnelling device 51 arranged downstream of the shaping rollers 50. In the funnelling device 51, the web 1 is further shaped into rod-shape, for example by gathering or pushing together. Preferably, when leaving the funnelling device 51, the web 1 has not yet achieved its final form, or is not entirely gathered, respectively. This facilitates the introduction of an object, such as a capsule or flavoured thread 71, into the endless rod of web material. A flavour application system 7 comprising an endless thread 71 and a flavour reservoir 72 is arranged downstream of the shaping device. The thread 71 is mounted on a bobbin 70. Preferably, the flavour reservoir 72 contains menthol. The thread 71 is unwound from the bobbin 70 and entrained with flavour before being transported to the gathered web 1. The flavour application system 7 may be provided with at least one of a flow meter, a valve, a temperature control and a pump for control and provision of a defined amount of flavour to be applied to the thread 71. The flavour application system 7 is arranged above the web 1 in order for gravity to support the introduction of the thread into the web. Gravity may also support a flow of flavouring liquid along the thread 71. Alternatively, or in addition, flavour may be added separately from the thread 71 or may be entirely omitted. In that case, the presence of the thread may have mostly an aesthetic contribution to the aerosol-generating article.

An endless wrap material 6, for example paper, is provided on a bobbin 60 and supplied from below the endless rod such that the endless rod of web material comes to lie on the wrap material 6. The wrap material 6 runs parallel to the endless rod when being joined with the rod. Before the wrap material 6 and the endless rod are joined, the wrap material is provided with glue. A glue reservoir 62 is in fluid connection with a seam nozzle 64 as well as with an anchor nozzle 63. Glue from the glue reservoir 62 is transported via a glue conduit, for example a tube, to the anchor nozzle and the seam nozzle. With the anchor nozzle 63, anchoring glue is applied to the wrap material, preferably, in a more central region of the wrap material 6. Preferably, anchoring glue is applied in lines transverse to the wrap material 6. The lines or anchoring glue, respectively, are provided for contacting the web material such that the wrapper is securely glued to the web material—thus the rod material is anchored in the wrapper. With the seam nozzle 64, seam glue is applied to the wrap material 6, preferably, along a lateral side of the wrap material 6. Preferably, the seam glue is applied in one longitudinal line, preferably one continuous line. The longitudinal line is provided for gluing the wrap material to itself after the wrap material has been entirely wrapped around the endless rod of web material. Thus, the wrap material forms a secure and preferably continuous seam.

Preferably, the glue reservoir 62 contains a liquid glue, which may be used for both the anchoring and the seaming of the wrap material. However, if different glue shall be used, a reservoir each for the anchoring and for the seaming may be provided. Different glues may be advantageous, for example, if a wrap material is a paper wrapper and paper glue shall be used for the seam and if, for example, specific plastics glue shall be used for the anchoring of the wrapper to a plastics web material of the endless rod. Also, glues may vary with respect to the settling time for the glue. For example a polyurethane glue and a hot-melt glue may be used for different purposes.

The so wrapped endless rod of web material may be guided in a rod-shaped bed 52 passing a heating device 53 for heating the wrapped endless rod. The heating facilitates a distribution and fast drying of the glue. After the endless rod has been formed, it is cut in the cutting device 8 into rod segments of predefined length, for example single or double length segments (having the length or the double length of a final product). The rod segments may be transported to a tray or storage 91. The rod segment may also directly be transported to a combiner 92 for being combined with further elements, for example further filter elements or segments of, for example, aerosol generating articles.

An online control unit 90 is provided after the endless rod has been cut into segments for a quality control of the manufactured segments. At the location of the tray 91, there may be provided an offline control unit 93. An online control unit 90 and offline control unit 93 may, for example, include a length control, diameter control, a weight control, ovality control, a control of the resistance to draw (RTD), the thread centering and other visual quality aspects of the semi-finished or finished good. The offline control unit 93 may for example also be provided with a measuring device for a menthol content or other substances in the rod segment. In the tray 91, the segments may be labelled, for example with a batch number, production date or product code, for example, for tracking of the products.

Preferably, tension rollers 30 and driving rollers 31 are provided in the apparatus for a controlled transport of the web of material 1 and a continuous, preferably constant, tensioning of the web. Synchronization means may be provided between crimping device 4 and a transport means such as a continuous belt, for example, at the position of the online control unit 90. By the synchronization means a linear speed of the endless rod and of the yet to be gathered substantially flat continuous material fed into the crimping device 4 may be synchronized.

Instead of having an apparatus, where the corona treatment is performed inline, a base material may also be corona treated previously and then supplied to the filter making apparatus.

FIG. 2 schematically shows a semi-finished product manufactured from rod segments, for example as produced in an apparatus similar as shown in FIG. 1, however without the corona module and without corona treating of the PLA foil. Two rod segments comprising a plug of PLA foil 1 wrapped with a paper wrapper 6 are aligned with their longitudinal axis with a further rod-shaped segment 11 arranged in between the PLA plugs. The further rod-shaped segment 11 may be a further filter element or may also be a plug of an aerosol-forming substrate, for example a tobacco plug. The further rod-shaped segment 11 is a double segment and combined with the two rod segments with an additional wrapper 13. During the combining step, the weak adhesion between PLA plug 1 and paper wrapper 6 makes the plug shift in the wrapper 6 by a shift distance 12. Such a shift distance may be up to a several millimetres. If a shift distance 12 is above a predefined distance, the product is typically regarded as being defective and will be removed.

In FIG. 3 a PLA film 1 is guided through a corona module 2 comprising two corona module portions 21, 22. The PLA film may be guided via guide rollers 200 into and out of the corona module 2. The set-up of the two corona module portions 21, 22 is substantially identical. The two corona module portions 21, 22 are arranged such that the PLA film is guided through the module portions 21, 22 in an s-form such that one side of the PLA film is corona treated in the first module portion 21. The other side of the PLA film is corona treated in the second module portion 22 arranged downstream and subsequently to the first module portion 21. A corona module portion 21,22 comprises a transport drum 20,23 as a counter-electrode. Preferably, transport drum 20,23 is at ground potential. The PLA foil 1 substantially performs a U-turn and lies closely against the transport drum 22,23 when being guided around the transport drum 20,23. A corona module portion also comprises an electrode 212,222 connected to a power generator unit 211,221 providing power and frequency of a voltage applied to the electrode 212,222. Electrode 212,222 and power generator 211,221 are arranged in a housing 210,220. The housing 210,220 is movably mounted for being moved away and towards the transport drum 20,23 for mounting and maintenance purposes. Preferably, the distance between electrode 212, 222 and counter electrode 20,23 may be set by the movable housing 210,220. The retracted positions of the housing is indicated with dotted lines 2100,2200. The electrode 212,222 comprises a concave shape corresponding to the circumference of the transport drum 20,23. The PLA foil 1 is guided between electrode 212,222 and counter electrode 20,23 and may thereby be corona treated on the side of the PLA foil facing the respective electrode.

In FIGS. 4a and 4b sections of an endless wrap material 6 are shown. Individual strips of adhesive 630 are applied along the width 602 of the wrap material 6. The strips 630 are intended for an anchoring of the wrap material 6 to the web material 1. The strips 630 do not extend entirely up to the lateral edges of the wrap material, such as not to cover a seam region for a wrapper seam or a seam glue line applied in the seam region, respectively. However, when being wrapped around a rod-shaped PLA plug, the strips preferably extend along the entire circumference of the PLA plug.

If the anchoring strips 630 are also used for a seam of the wrap material 6, the strips may also extend up to the lateral edges of the wrap material.

The strips 630 are applied and distributed along the length of the wrap material. Preferably, they are arranged equidistantly over the length of the wrap material 6. Individual wrapper segments 601 are indicated by cutting lines 80,81. The cutting lines 80,81 correspond to a position the endless rod is subsequently cut into rod segments. Preferably, a strip pattern has predetermined values of, for example, the distances between strips, the number of strips and the width of strips. Preferably, the predetermined values are selected according to a length 603 of an individual wrapper segment 601.

In FIG. 4a , two strips 630 per wrapper segment 601 are provided, while the wrap material 6 is cut between strips. In FIG. 4b , only one strip 630 at half length of the wrap material 6 per segment is provided.

A width 602 of the wrap material 6 may be between 23 millimeter and 30 millimeter, for example 28 millimeter. A length 603 of the individual wrapper segments may be between 8 millimeter and 20 millimeter, for example 12 millimeter. A width between strips 630, where one strip per wrapper segment is provided is preferably identical to a wrapper segment length 603. However, all these values may be adapted to a cross section and length of a rod segment to be cut from the endless rod of web material and to be wrapped in a wrapper segment 601.

FIG. 5 shows a measurement set-up for measuring an anchoring of a PLA rod 1 in its plug wrapper 6. For this measurement the wrapped PLA plug is pierced onto a pin 18 provided with an extended base. An adhesive tape 18 is attached to the wrapper 6. Preferably, the adhesive force between adhesive tape 18 and wrapper 6 is stronger than an adhesive force between wrapper 6 and PLA plug 1. Pin 1 and adhesive tape 18 are each fixedly held in a force measurement device 16, for example, dynamometer grip cells. The two dynamometers pull at the tape and the plug in opposite directions as indicated by arrows 17.

In FIG. 6 results of PLA anchoring measurements performed with the set-up as shown in FIG. 5 are depicted. FIG. 6 shows that the anchoring strength can be improved by the corona treatment, when comparing samples of non-corona treated PLA foil 15 and corona treated PLA foil 65. Routinely, a doubling or tripling of the anchoring strength may be achieved by the corona treatment of the PLA foil. An additional effect is apparent between different glue patterns 631 provided on the paper wrapper 6. Random spiral, double longitudinal strips and square or transverse strips show enhanced anchoring compared to the commonly used single longitudinal strip 170. If corona treatment is combined with a dedicated glue pattern, anchoring strength may significantly be enhanced and a number of defective products may significantly be reduced.

The amount of defective semi-finished products (as shown in FIG. 2) comprising non-corona treated polylactic acid foil glued to a paper wrapper provided with one longitudinal glue line along the central axis of the wrapper have been compared with the amount of defective semi-finished products comprising corona treated polylactic acid foil glued to a paper wrapper provided with glue strips extending transverse to the wrapper. Products were identified as defective if the shift distance 12 between PLA plug 1 and wrapper 6 amounted to more than 1 millimeter. Comparison showed that the number of defective products could be reduced by about 120 times (29 defective semi-finished products per one tray 91 compared to one defective semi-finished product per four trays 91). 

1. Method for manufacturing a wrapped endless rod of substantially flat continuous material, the method comprising the steps of: providing a substantially flat continuous material; treating the substantially flat continuous material with corona discharge; forming the corona treated substantially flat continuous material into an endless rod; providing a wrapper; applying adhesive to the wrapper, and wrapping the endless rod with the wrapper, wherein the step of applying adhesive to the wrapper comprises applying adhesive over a width of the wrapper and in a central longitudinal portion of the wrapper, and comprises applying the adhesive in several strips over a length of the wrapper.
 2. Method according to claim 1, comprising the step of guiding the substantially flat continuous material between electrode and counter electrode of a corona module.
 3. Method according to claim 1, corona treating the substantially flat continuous material during a treatment time in a range between 0.001 seconds and 2 seconds.
 4. Method according to claim 1, comprising the step of corona treating one side of the substantially flat continuous material and subsequently corona treating the other side of the substantially flat continuous material.
 5. Method according to claim 1, wherein a strip of adhesive is applied along the longitudinal central axis of the wrapper.
 6. Method according to claim 1, wherein several strips are arranged in parallel.
 7. (canceled)
 8. (canceled)
 9. Method according to claim 1, wherein the substantially flat continuous material is a plastics material, for example polylactic acid.
 10. Method according to claim 1, applying one type of adhesive to the central longitudinal portion of the wrapper and another type of adhesive to a seam portion of the wrapper.
 11. Consumable comprising a segment of a wrapped endless rod manufactured according to the method according to claim
 1. 12. (canceled)
 13. Apparatus for manufacturing a wrapped endless rod of substantially flat continuous material, wherein the apparatus is programmed to perform the method according to claim 1, the apparatus comprising: a rod-forming unit for shaping a substantially flat continuous material into an endless rod; a wrapping device for providing a wrapper and for wrapping the endless rod with the wrapper; an adhesive applicator for applying an adhesive to the wrapper, wherein the adhesive applicator is arranged for applying adhesive to a central portion of the wrapper; a corona module arranged upstream of the rod-forming unit for corona treating the substantially flat continuous material.
 14. Apparatus according to claim 13, wherein an electrode of the corona module has a lateral size corresponding to a width of the substantially flat continuous material to be corona treated.
 15. Apparatus according to claim 13, wherein a distance between electrode and counter electrode is in a range between 0.1 millimeter and about 25 millimeter.
 16. Apparatus according to claim 13, wherein the corona module comprises a first module portion and a second module portion, the first module portion and the second module portion each comprising an electrode-counter electrode pair, wherein the electrode-counter electrode pair of the first module portion is arranged and powered to enable corona treatment of one side of the substantially flat continuous material and the electrode-counter electrode pair of the second module portion is arranged and powered to enable corona treatment of the other side of the substantially flat continuous material.
 17. Apparatus according to claim 16, wherein at least one module portion comprises two electrodes arranged next to each other in a transport direction of the substantially flat continuous material.
 18. Apparatus according to claim 13, wherein the corona module comprises a high frequency generator for providing frequencies in a range between 10 kHz and 60 kHz and an alternating voltage between 15 kV and 40 kV. 